Merge pull request #408 from talpor/master

Properly handles a scenario when an instance's PK is None

src/reversion/revisions.py

@@ -179,6 +179,7 @@ def end(self):
                                 (obj, callable(data) and data() or data)
                                 for obj, data
                                 in manager_context.items()
+                                if obj.pk is not None
                             ),
                             user = self._user,
                             comment = self._comment,